chore: build with hatchling only and move MCP deps to an extra

[SkyeAv]

Consolidates the project on a single hatchling build via pyproject.toml and moves the MCP server dependencies into an optional mcp extra, so a base install of TCT no longer pulls in the MCP stack.

Build system

• Single backend: deletes the legacy setup.py (setuptools) and the stale root requirements.txt; pyproject.toml (hatchling) is now the only build source of truth. setup.py had drifted to 0.1.6 and even listed the stdlib copy module as a dependency.
• Wheel unchanged: reuses the existing [tool.hatch.build.targets.wheel] packages = ["TCT"]; the wheel still ships exactly the TCT/ modules.

MCP extra

• New extra: adds [project.optional-dependencies] mcp = ["fastmcp>=2.12.2", "click>=8.2.1"] and removes both from the required dependencies.
• Clean split: only TCT/server.py imports fastmcp/mcp, and TCT/__init__.py never imports the server, so the core package imports fine without the extra.
• click included: it was only present to satisfy fastmcp and isn't imported anywhere in TCT/, so it moves into the extra too.

Dev/CI ergonomics

• Makefile: install now runs uv sync --all-extras --dev, matching .github/workflows/main.yml, so local dev installs the mcp extra and tests/test_server.py runs.
• Test guard: tests/test_server.py now starts with pytest.importorskip("fastmcp"), so a no-extras install skips the module instead of erroring at collection.
• Lock: uv.lock regenerated; this also corrected the locked project version from the stale 0.1.6 to 0.2.0.

Design

• Why an extra: the MCP server is a thin wrapper over the core toolkit; an optional extra keeps one distribution while letting non-MCP consumers avoid fastmcp/mcp and their transitive deps.
• Deferred: the pre-existing tct-server = "main:main" console script points at root main.py, which the hatchling wheel (packages = ["TCT"]) does not ship — so the installed script won't resolve. Left out of scope; worth a follow-up to move the entrypoint to TCT.server:main.
• Accepted caveat: TCT/.ipynb_checkpoints/ is git-tracked (Jupyter autosave) and was not touched here.

Testing

• uv build → Successfully built dist/tct-0.2.0.tar.gz and dist/tct-0.2.0-py3-none-any.whl.
• unzip -p dist/tct-*.whl tct-0.2.0.dist-info/METADATA → Provides-Extra: mcp, Requires-Dist: fastmcp>=2.12.2; extra == 'mcp', Requires-Dist: click>=8.2.1; extra == 'mcp'.
• Fresh venv, base wheel → import TCT OK; fastmcp installed? False.
• Fresh venv, wheel[mcp] → import TCT.server OK; fastmcp/click present; mcp.name == "translator-toolkit".
• uv sync --all-extras --dev && uv run pytest tests/test_server.py -v --no-cov → 3 passed.
• No-fastmcp venv, pytest tests/test_server.py → 1 skipped (could not import 'fastmcp').
• uv run ruff check tests/test_server.py → All checks passed! (the 19 repo-wide ruff errors are pre-existing in TCT/ sources, untouched here; CI runs ruff with continue-on-error).

Questions for the reviewer

• tct-server script. Fix the broken console script (move the entrypoint to TCT.server:main) in a follow-up, or fold it into this PR?

[SkyeAv]

Should I rerun tests if they're failing because node norm and such seem to be down?